This is just a quick note for anyone else out there who recently ran brew update && brew upgrade and then found that Python no longer worked as expected. Here are the important points:

• The issue is that Homebrew introduced a breaking change and did a crappy job of documenting it.
• The fix is to prefix your path with /usr/local/opt/python/libexec/bin
• More details can be found at https://github.com/Homebrew/homebrew-core/issues/15746

For me, the fix was to add this to my .zshrc file:

export PATH="/usr/local/opt/python/libexec/bin:$PATH"